Field of the Invention
The present invention relates to a switching regulator, and particularly to a switching regulator equipped with a power supply monitoring circuit which monitors a power supply voltage Vin to prevent a malfunction.
Background Art
A switching regulator may have the generation of a large current and a high voltage in its output by a malfunction of an internal circuit thereof when a power supply voltage Vin is significantly reduced. In order to prevent it, the switching regulator is equipped with a power supply monitoring circuit.
FIG. 7 is a circuit diagram illustrating a related art switching regulator. A PMOS transistor 3 being a switching element performs switching according to a control signal inputted thereto. An inductor 5 and an output capacitor 6 smooth a voltage subjected to the switching. A diode 4 makes a current to flow when the PMOS transistor 3 is off. An output control circuit 15 performs switching control on the PMOS transistor 3 in such a manner that an output voltage thereof becomes a prescribed constant voltage. An RS-FF circuit 13 outputs a signal to the output control circuit 15, based on a signal of an error comparator 10 and a signal of an on-time control circuit 11. The error comparator 10 outputs the signal to the RS-FF circuit 13, based on a reference voltage of a reference voltage circuit 12 and a feedback voltage of a voltage division resistance circuit 17.
A power supply monitoring circuit 40 monitors a fluctuation in the power supply voltage Vin and outputs a detected signal to the output control circuit 15 when the power supply voltage Vin becomes lower than a prescribed voltage. When the output control circuit 15 receives the detected signal from the power supply monitoring circuit 40, the output control circuit 15 outputs a signal of an H level to stop the PMOS transistor 3.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-328589
However, there is a need to improve the power efficiency while securing safety in the switching regulator.